The present invention is directed to the provision of a thin coat of encapsulant on the top surface of an electrical device such as a semiconductor chip having bumps on the top of the chip bonded to an electrical interconnect medium such as the inner leads of a tape automated bonded (TAB) tape frame. The purpose of the coating is to provide mechanical scratch protection for the passivation layer of the device, mechanical support for the inner lead bonds, and shielding from gross chemical contamination. Several prior art processes which have been suggested for higher density packaging and replacement of standard molded single chip packages are (1) a "glob" coating of a high viscosity liquid encapsulant or (2) a thin coating of a low viscosity liquid encapsulant, both applied to the top surface of the chip forming a single top coating. A single top coating has the advantage of protecting the chip while allowing for higher density packaging and for direct cooling of the chip through its back side thus not thermally insulating the chip. However, the prior art processes possess many disadvantages. The application of a high viscosity material as a "glob" coating produces a coating which is very thick in the center (typically 20 to 50 mils) and thin at the edges, while the application of low viscosity or solvent cut materials produce a coating which is undesirably thin at the edges and which drips to the back side of the chip. The addition of solvents requires extra processing for removal and may cause bubbling. Both of these processes lack the ability to control the material coverage which result in running, nonplanarity, no shape control, no thickness control, and incomplete surface coverage particularly in the corners. These materials utilized in combination with the lack of dimensional flow control for these processes result in inferior reliability particularly for larger devices due to large thermal stresses induced on the device.
The present invention is directed to encapsulating the top of a chip after inner lead bonding and prior to outer lead bonding and is directed to dispensing a thin coating of a high viscosity liquid encapsulant as a semi-planar, for example, plus or minus 1.5 mils, coating with a controlled average thickness, preferably between 3 and 6 mils. The encapsulant completely covers the entire top surface of the chip including the corners and the area around and beneath the inner lead bonds.